1. Field of the Invention
This invention relates to a semiconductor device having a metalized multi-layer interconnect and a method for manufacturing the semiconductor device.
2. Description of Related Art
Interconnection metalizations for interconnects of semiconductor devices, are typically formed by a single layer of an aluminum alloy, or are multi-layer metalizations. Known multilayer metalizations are composed of a bottom, refractory metal layer, such as TiN, TiW, or the like, serving as a diffusion barrier layer, and a top aluminum alloy layer. Reductions in the size of semiconductor devices has led to the use of a further metal nitride layer as a top layer of an aluminum alloy interconnect. Use of a top metal nitride layer in this manner can serve, among other purposes, to prevent irregular reflection from the aluminum alloy layer in photolithographic processes, and to prevent the occurrence of hillocks. A metal nitride layer may be formed on an aluminum alloy layer by a reactive sputtering process.
In such interconnection metalizations for semiconductor devices, a lower resistance at the boundary of the aluminum alloy layer and the metal nitride layer is desirable. However, if the surface of an aluminum alloy layer is exposed to an atmosphere containing oxygen, while the metal nitride of the top layer is being formed by reactive sputtering, an oxide layer will form on the surface of the aluminum alloy layer. Such an oxide layer serves to electrically insulate the metal nitride from the aluminum alloy. Even when the interconnection metalization is formed in a vacuum chamber, the surface of the aluminum alloy layer is nitrided by exposure to a nitrogen plasma during the reactive sputtering, which increases the electrical resistance of the boundary between the metal nitride and aluminum alloy layers.
Tests have been performed on a triple layer interconnect composed of respective layers of titanium nitride, aluminum alloy, and titanium nitride (TiN/Al alloy/TiN), to measure the effect of the bottom nitride layer on electrical resistance and electromigration. In a double layer interconnect, formed of a bottom aluminum alloy layer and a top titanium nitride layer (TiN/Al alloy), a discontinuity in the aluminum alloy layer, such as would be caused by electromigration, results in a sudden failure of the interconnect (an open circuit).
When the triple layer interconnect was tested, a sudden failure of the interconnect did not result, because the lower titanium nitride layer served as a current path. However, the bottom nitride layer serves not only as an alternate current path, but also as a diffusion barrier into which atoms diffuse from the substrate below. As a result of such diffusion, the electrical resistance of the bottom nitride layer, and thus of the current path, gradually increased until the interconnect failed.